The summit was attended by an invited audience of foreign dignitaries, car industry representatives and environmental groups aimed at promoting the development of zero and low emission vehicles in the UK and overseas.

During his address, Dr Speth issued an impassioned defence of diesel cars, which have been seen as one of the major sources of air pollution in European towns and cities. Dr Speth claimed that newer diesel models are ‘cleaner than many petrol cars’ and criticized government for failing to implement policies designed to remove older, more polluting diesel cars from the road.

He said: “Public policy sometimes seems to know what it is against, not what it is for. The restrictions on diesel make the point.

“The diesel vehicles we produce to EU 6 standards are some of the cleanest cars ever made. They are as clean as petrol and produce 25-30% less CO2. Yet, they are demonised.

“No incentive has been put in place to change from older polluting cars, but the disincentive has been placed on the newer, cleaner models through tougher regulations and higher taxation. The resulting impacts are as significant as forecast.”

He added: “The internal combustion engine is far from being obsolete. It is a state of the art technology that we strive to refine and improve.”

‘Innovation’

Speaking after Dr Speth, the Prime Minister described the transition to cleaner vehicles as “one of the most pressing issues in transport.”

Prime Minister Theresa May speaks at the Zero Emission Vehicle Summit

She said: “Electrification, self-driving cars, delivery drones and electric cargo bikes – will all help reduce traffic, improve journey times and safety, and free-up space in our towns and cities.

“But innovation will also clean up our air – and that is why we are here today, at this, the UK’s first zero-emission vehicles summit.

“How we accelerate the transition to zero-emission vehicles – and ensure cleaner air for all our people – is one of the most pressing issues in modern transport.”